It has been usual in conventional apparatus of this kind for continuously supplying a hot blast at a required temperature, to supply a hot blast at a temperature higher than the required temperature and to mix this hot blast with cooling air to equalize its temperature.
This conventional arrangement, however, is deficient in that a regenerative layer within the stove must be comparatively great in height so that the minimum temperature of the hot blast obtained at the end of the blast supply period of time is above the required temperature. Additionally, a control means is required for adjusting the supply of blast gas and cooling air to maintain the required temperature.